Primary cell and anode for use therein



June 5, 1962 J. L. ROBINSON PRIMARY CELL AND ANODE FOR USE THEREIN 2 Sheets-Sheet 1 Filed Nov. 3, 1958 EFFECT OF Al AND Zn LEVELS ON ANODE EFFICIENCY 40H M GENERAL PURPOSE 956a 0.//o a2 7 5 /2 /f 0 N I 2 [N n 5 n/ 0 2 5 n/ am 0 O wwwm fl/uminum EFFECT OF Al AND Zn LEVELS ON MAXIMUM DELAYED ACTION 4 OHM GENERAL PURPOSE 70 fl/um/num HGEIVT June 5, 1962 J. ROBINSON 3,038,019

PRIMARY CELL AND ANODE FOR USE THEREIN Filed Nov. 3, 1958 2 Sheets-Sheet 2 IN V EN TOR. John L. Rabin son K' Q Q. @7014) HGENT United States Patent PRIMARY CELL AND AN ODE FOR USE THEREIN John L. Robinson, Freeland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Nov. 3, 1958, Ser. No. 771,652 6 Claims. (Cl. 136-83) This invention relates to battery anodes and particularly to magnesium alloy anode metals for use in primary cells.

For many years those skilled in the art of making primary cells in which a magnesium alloy has been used as the anode material have endeavored to increase the efliciency of the anode metal (get an ever larger number of ampere hours output per pound of alloy), and to shorten the delayed action time (the delay between the time the primary cell is put into a circuit and the time the cell delivers an operating potential into the circuit).

Considerable progress has been made both in increasing anode efiiciency and in reducing the delayed action time of magnesium anode primary cells, but further progress is desired.

In the course of research in connection with the use of magnesium alloys as anode material in a primary cell it was found that magnesium alloys containing zinc and aluminum were preferred for such usage. It was found that by increasing the aluminum level of the alloy to 3 or 3 weight percent thereof that anode efliciency could be increased substantially. It was also believed that as the aluminum level of the alloy increased, irrespective of the zinc level in the alloy, that the delay time increased.

In other words those skilled in the art followed, as a rule of thumb, for many yearsthe proposition that in a given alloy system increased delayed action and in creased anode efliciency went hand in hand. This assumption was based on the fact that the level of delayed action and the level of anode efiiciency are both believed to be dependent on the surface film formed on the cell anode during usage. It was assumed that the more coherent and impervious the film formed on the anode surface, the higher would be the anode efiiciency. It was also assumed that the delayed action time of the cell would increase as a function of resistance to the breakdown of the film.

Accordingly, a principal object of this invention is to provide an improved magnesium anode alloy which has inherently high anode efiiciency and low delayed action characteristics.

The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, in which:

FIG. 1 is a graph showing the effect of aluminum and zinc levels on anode efliciency of a magnesium anode alloy;

FIG. 2 is a graph showing the effect of aluminum and zinc levels on maximum delayed action in magnesium anode alloys, and

FIG. 3 is a side elevational view partly in section, showing a primary cell having an anode in accordance with this invention.

In accordance with this invention there is provided a magnesium alloy anode metal comprising 1.6 percent to 2.5 percent aluminum, zinc from one-half to one times the aluminum concentration (the aluminum/zinc ratio must be in the range of 1 to 2), up to .5 percent calcium, the balance being commercial magnesium containing not over .005 percent iron, not over .002 percent nickel and not over .1 percent manganese.

Referring to FIG. 1, it may be seen that in general as the aluminum content rises in magnesium alloys contain- 3,038,019 Patented June 5, 1962 ice 7 ing between .5 percent and 2.0' percent of zinc the anode efiiciency rises. The data for alloys having both .5 percent Zinc and 1.0 percent zinc lie so closely along the same line that only a single line for-alloys having these zinc content values has been plotted on the graph.

FIG. 2 shows that delayed action time is, in general, lower if the zinc content of the alloy is low. The 0.5 weight percent zinc line approaches zero delayed action time when the aluminum content of the alloy is about .4 weight percent. However, an anode made of such an alloy has low efficiency in the aluminum content range where low delay time occurs.

What has not been realized until this invention is that a range of aluminum content (with coordinated Zinc range) in an alloy exists in which an increase in aluminum content of the alloy (within limits) results in increased anode efiiciency and, unexpectedly, in a decrease in maximum delayed action time.

The maximum delay time in seconds rather than minimum or average delay time in seconds is used as the ordinate in the graph of FIG. 2 because maximum delay time value gives the one set of values which define the re liable delay performance characteristics of the anodes of a particular type.

The four ohm general purpose test used in compiling data used in the graph involved D size batteries discharged through a four ohm resistance, 5 minutes per day, 7 days per week, to a cut-off voltage of 1.2 volts per cell. Anode efiiciency is measured by weighing the anode before and after the completion of the test and dividing the actual weight loss into the theoretical weight loss (based on total ampere hours delivered by the cell) times 100.

While the broad range of aluminum-zinc values which define the invention has been listed above, it has been found that preferred results are obtained when the aluminum content of the anode alloy is between 1.6 and 2.0 weight percent, between 1.0 and 1.5 weight percent zinc, between .1 and .25 weight percent calcium, balance commercial magnesium with iron, nickel and manganese as stated above in reciting the broad range of the alloy of the invention. A preferred anode composition is 1.8 weight percent aluminum, 1.3 percent zinc, .15 weight percent calcium, balance commercial magnesium containing not more than .005 weight percent iron, .0 02 Weight percent nickel and .01 weight percent manganese.

The minimum aluminum concentration was established at 1.6 weight percent, as below this concentration low anode efi'iciencies (35 percent or below) resulted. On the other hand aluminum concentrations above 2.5 weight percent resulted in high delayed action. The zinc level should be controlled to give an aluminum, zinc ratio of between 1 and 2, as discussed above, to maintain acceptable anode efficiency and low delay.

The battery 10 shown in FIG. 3 illustrates a primary cell incorporating an anode 12 made in accordance with this invention. The battery 10 includes a coaxially disposed cathode electrode 14 within a cylindrical casing 16 which has a metal bottom 18. The anode 12, disposed between the cathode electrode 14 and casing 16, is electrically connected to the bottom 18 by means of a strip connector 20 which is secured to both the anode and casing bottom. The cathode electrode 14 is insulated from the bottom 18. A separator bag 22 filled with suitable cathode mix and electrolyte 24 encases the lower part of the cathode electrode 14 and is disposed against the anode 12. Above the anode a wax seal 26 extends across the casing 16 with the upper part of the cathode electrode 14 extending therethrough. A vent tab 28 extends through the seal 26 to vent gases generated as the cell is used.

Although only the above type primary cell is described it is Gbvious that the anode of this invention may be used in a wide variety of types of primary cells as well as several types of electrolytes and'cathode mixes.

Anodes made in accordance with this invention have been tested and show good results, for example, when used in cathode mix and bromide type electrolyte mixes as described in US. Patent No. 2,547,907 and also using sea water as an electrolyte.

Cells used in obtaining the test data recorded on the graphs, of the drawing were made with a cathode mix containing 87 percent lay-weight of manganese dioxide, 3 percent basic Zinc chromate, and 10 percent acetylene black to which wasadded 2.5 grams of powdered ma nesium per 1,000 grams of dry cathode mix. The dry mixture was Wetted with 410 cubic centimeters of electrolyte per 1,000 grams of dry cathode mix. The electrolyte contained 375 grams per liter of magnesiumbromide, 25 grams perliter of zinc bromide and .25 gram per liter of sodium chromate, the balance being water.

Similar resultshave, however, been achieved with other manganese dioxide depolarized cathode mixes moistened with aqueous solutions of chlorides or bromides of alkali earth metals.

. I claim: I p v v 1, An anodemetal for use in a primary cell comprising from 1.6 to 2.5 weight percent of aluminum, between .8

and 2.5 weight percent of zinc, the amount of Zinc in a' being substantially all magnesium.

2. An anode metal for use in a primary cell comprising from 1.6 to 2.0 weight percent of aluminum, between 1.0 and 1.5 Weight percent of zinc, the amount of zinc in" a given alloy being between one half and onetimes the amount of aluminum therein, between .1 and .25 weight percent'of calcium, not over .OOSWeight percent iron, not

over .002 weight percent nickel, and not over .1 weight percent manganese, the remainder being substantially all magnesium. a

3. An anode metal for use in a primary cell comprising 71.8 weight percentof aluminum, 1.3 weight percent of zinc, .15 weight percent of calcium, not over .005 weight percent iron, not over .002 weight percent nickel, and not over .1 weight percent manganese, the remainder being substantially. all magnesium. g

4. A primary cell comprising at least a cathode, electrolyte and an anode, said anode comprising from 1.6 to 2.5 weightpercent of aluminum, between .8 and 2.5 weight percent of zinc, the amount of Zinc in a given alloy being between one half and one times the amount of aluminum therein, between about .1 weight percent and .5 percentof calcium, not over .005 weight percent iron, not over .002 weight percent nickel, and not over .1 weight percent manganese, the remainder being substantially all magnesium.

5. A primary cell comprising at least a cathode, electrolyte and an anode, said anode comprising from 1.6 to 2.0 weight percent of aluminum, between 1.0 and 1.5 weight percent of zinc, the amount of zinc in a given alloy beingbetween one half and one times the amount of aluminum therein, between .1 and .25 Weight percent of calcium, not over .005 weight percent iron, not over .002 weight percent nickel, and not over .1 weight percent manganese, the remainder being substantially all magnesium.

6. A primary cell comprising at least a cathode, electrolyte and an anode, said anode comprising 1.8 weight percent of aluminum, 1.3 weight percent of zinc, .15 Weight percent of calcium, not over .005 weight percent iron, not over .002 weight percent nickel, and not over 1 weight percent manganese, the remainder being substantia'lly all magnesium.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN ANODE METAL FOR USE IN A PRIMARY CELL COMMPRISING FROM 1.6 TO 2.5 WEIGHT PERCENT OF ALUMINUM, BETWEEN .8 AND 2.5 WEIGHT PERCENT OF ZINC, THE AMOUNT OF ZINC IN A GIVEN ALLOY BEING BETWEEN ONE HALF AND ONE TIMES THE AMOUNT OF ALUMIUM THEREIN, BETWEEN ABOUT .1 WEIGHT PERCENT AND .5 WEIGHT PERCENT OF CALCIUM, NOT OVER .005 WEIGHT PERCENT IRON, NOT OVER .002 WEIGHT PERCENT NICKEL, AND NOT OVER .1 WEIGHT PERCENT MANGANESE, THE REMAINDER BEING SUBSTANTIALLY ALL MAGNESIUM. 